A.P. Jenkins

Microstrip disk resonators for filters fabricated from TBCCO thin films

Microstrip disk type resonators have been designed and tested. These have been fabricated from TBCCO 2212 thin films deposited by DC sputtering onto 2 cm square LaAlO/sub 3/ substrates. The R/sub s/ of such large area films has been measured at 40 GHz using a copper end wall replacement cavity and shown to be less than 200 /spl mu//spl Omega/ scaled to 10 GHz and at 80 K. Q values of 2 to 6 GHz disk resonators have demonstrated considerable improvements when compared to both linear HTS microstrip resonators and comparable copper disk resonators. Additionally, preliminary results for the performance of such disk resonators as a function of microwave power will be presented for application in high power filters.

Transmission characteristics of HTS microstrip resonators with a ferrite component

Microwave transmission characteristics of HTS microstrip resonators containing a monocrystalline ferrite layer magnetized in an arbitrary direction were calculated using a RCL approach. Dependencies of the resonance frequencies on the external magnetic field strength and the field orientation angles were analyzed and the results of the calculations were compared with the experiment.

Synthesis and microwave characterisation of DC sputtered Tl-Ba-Ca-Cu-O thin films

Single- and double-sided superconducting Tl-Ba-Ca-Cu-O thin films (2- mu m thick) have been prepared on MgO

A miniaturized interdigital microstrip bandpass filter

A 2.4 GHz three-stage microstrip bandpass filter was designed using a miniaturized interdigital capacitor structure to reduce the configuration in size. The filter was simulated by a finite element method software and then fabricated using TBCCO superconducting films on 20 mm/spl times/20 mm/spl times/0.5 mm MgO substrates. It was generated by photolithographic and wet etching process and packaged in a brass box. The bandwidth is 4% and the passband insertion loss of the filter was measured to be -0.4 dB at 77 K. The return loss is better than -8 dB. In particular, this filter has a sharper performance at its edge of fundamental pass band.

Tl-Ba-Ca-Cu-O thin films on buffered substrates for microwave device applications

Tl-Ba-Ca-Cu-O thin films have been grown on a variety of substrates, both with and without the use of buffer layers. Differences in processing routes required for the various film-substrate combinations are highlighted and the effect of the buffering layers on the microstructure, transport and microwave properties of the films are discussed.

The microstructure and electrical properties of thin films processed at low temperatures

thin films on (001) with excellent alignment suitable for microwave applications at 77 K have been fabricated using an ex situ anneal step in argon atmospheres at temperatures of . Surface resistance values as low as 400 (79 K, 10 GHz) and large-area critical current densities up to (77 K) have been achieved. In order to understand the relationship between the microstructure and electrical properties the films have been characterized by a variety of techniques, but especially transmission electron microscopy and allied methods. Microstructural features such as a-axis oriented grains, secondary phase particles, grain boundaries and surface outgrowths (especially of non-superconductor phases) have been found to have a significant effect on the surface resistance.

Application of TBCCO based HTS devices to digital cellular communications

Linear microstrip resonators suffer from high peak current density inside the resonators which limit the power handling characteristics and hence their use in cellular transmitter applications. To realise higher power filter and combiner networks for cellular applications it is possible to use two dimensional microstrip resonators (such as disks) to equalise the internal current distribution. We have designed and tested such microstrip resonators, fabricated from TBCCO 2212 thin films deposited by RF sputtering onto 50 mm diameter LaAlO/sub 3/ substrates. The R/sub s/ of such films has been measured at 5.5 GHz using a sapphire dielectric resonator and shown to be less than 1 m/spl Omega/ scaled to 10 GHz and at 80 K. The power handling of disk resonators designed for operation in the PCS and DCS1800 cellular bands has been shown to be superior to that of linear resonators fabricated from similar material. The operation of such devices using high power levels and realistic signals encountered in 2/sup nd/ generation digital cellular systems (e.g., DQPSK and GMSK) will be presented. The application of these devices to 3/sup rd/ generation wide band CDMA systems will also be discussed.

Microstructural Studies of Tl2Ba2Ca2Cu3Ox Thin Films on LaAlO3 and MgO Substrates.

Tl2Ba2Ca2Cu3Ox thin films have been fabricated on (001) LaAlO3 and (001) MgO substrates. Films grown on LaAlO3 have Tc=112K and RS(80K, 10GHz)=0.2mΩ, while films on MgO have Tc=117K and Rs(80K, 10GHz)=0.7mΩ. The grain size and alignment of the films has been investigated using X-ray diffraction, Scanning Electron Microscopy and Electron Backscattered Diffraction. We show evidence for a markedly higher in-plane angular spread for films on MgO and believe that for films grown on this substrate the lowest achievable values of Rs are limited by disorder in the in-plane alignment of the TBCCO film caused by the large lattice mismatch between the materials.

Study of the magnetic tuning effect in HTS coplanar resonators

Formulae for calculating the resonance frequency and the microwave (MW) losses in HTS thin film coplanar waveguide resonators containing a tangentially magnetized ferrite layer were obtained using the perturbation method. The problem of achievement of a maximum sensitivity of the resonance frequency to the field intensity and the problem of reducing the MW losses contributed to the resonator by the magnetostatic waves were analysed.

Microstructural and microwave characterisation of low temperature processed Tl/sub 2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ thin films

Tl/sub 2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ thin films on LaAlO/sub 3/ with excellent alignment suitable for the fabrication of passive microwave devices operating at 77 K are fabricated using an ex-situ anneal step in argon atmospheres at temperatures of 720-740/spl deg/C. In order to understand the factors influencing their microwave and transport properties, the microstructure and compositions of the films have been examined by TEM, HREM and SEM and correlated with R/sub s/ measurements obtained by the partial-end-wall-replacement technique.